# How to define x and y as functions of time?

NathanielCunningham shared this question 2 years ago

I would like to use Geogebra (graphing calculator or Classic I suppose) to help students visualize constant acceleration motion in physics, for example projectile motion in constant gravity. We want to define position components x(t) and y(t) as functions, and plot them with respect to time t.

We would define constant values for initial position and velocity x_0, v_x, y_0, v_y0, and constant acceleration a_y=-9.81.

Then we would define functions x(t), y(t), v_y(t) using these constants, and graph x vs. t, y vs. t, v_y vs t.

Unfortunately when I try to name a function "x" by typing

`x(t) = x_0 + v_x*t`

I get "eq1 undefined"

A function named "x_p(t)" works, but deviating from a well-established convention is undesirable.

is there a way to do what I am after?

1

x and y are predefined (standart) functions in GeoGebra and they are used to find the x-coordinate and y-coordinate of a point, respectively. I mean they assumes a point as input and produces the x-coordinate and y-coordinate of this point as the outputs. Therefore you need to use different names for the position functions in your work. But you can still show their labels as x(t) and y(t) by entering these names in the caption field of these functions and then selecting the label as caption.

1

you can define X(t) not x(t)

1

Ah, the capital X is an improvement over subscripts, thanks for that!